<template>
    <ul class="list">
       <li
           class="item"
           v-for="item of letters"
           :key="item"
           :ref="item"
           @touchstart.prevent="handleTouchStart"
           @touchmove="handleTouchMove"
           @touchend="handleTouchEnd"
           @click="handleLetterClick"
           >{{item}}</li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cityes: Object
    },
    computed: {
        letters () {
            const letters = []
            for (let i in this.cityes) {
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus: false,
            startY: 0,
            timer: null
        }
    },
    updated () {
       this.startY =  this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = true
        },
        handleTouchMove (e) {
            if(this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(() => {
                    const touchY = e.touches[0].clientY - 74
                    const index = Math.floor((touchY - this.startY) / 22)
                    if (index >= 0 && index < this.letters.length) {
                        this.$emit('change',this.letters[index])
                    }
                }, 16);
            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
    @import '~styles/varibles.styl'
    .list
        display:flex
        justify-content: center
        flex-direction: column
        position: absolute
        right: 0
        top: 1.58rem
        bottom: 0
        width: .4rem
        .item
            line-height: .44rem
            color: $bgColor
            text-align: center
</style>